The present invention relates generally to input/output communication. More particularly, the invention is a method and apparatus for controlling data flow through a group of first level memory device controllers and a group of second level memory device controllers such that if one of the second level memory device controllers experiences a failure, rerouting of data can be accomplished transparently to the computer.
Systems for controlling data flow between a computer and a group of memory devices typically include at least one controller situated between the computer and the memory devices. The controller is used to handle data communication between the computer and the memory devices. Computer systems can be configured to include a group of memory devices. Each such controller is assigned a particular group of memory devices. As data is output from the computer a particular controller will handle that data and store it in one of the memory devices under its control. Through the use of these controllers and the physical configuration of the memory devices, the logical configuration of the memory devices can be altered and set to the needs of the user.
In the case where one of the controllers experiences a failure, the computer must take action to isolate the failed controller and to switch the memory devices formally under the failed controller's control to a properly functioning other controller. The switching requires the computer to perform a number of operations. First, it must isolate the failed controller. This means that the path between the computer and the failed controller must be broken and all data flow directed to the failed controller must be redirected to a working controller.
In the system described above, it is necessary for the computer to be involved with rerouting data away from a failed controller. The necessary operations performed by the computer in completing rerouting requires the computer's attention. This places added functions on the computer which may delay other functions which the computer is working on. As a result, the entire system is slowed down.